This invention relates to an axial fan and especially to an electrically driven fan comprising a fan wheel with blades or fins, the tips of the fins being connected to a surrounding ring.
Such fans are known to be used in blowers of water-cooled vehicle engines, the blowers being arranged between the radiator and the engine unit. Fresh air is sucked in by means of the fan wheel, passed through the radiator and discharged to the exterior. The normal practice is to take the cooling air axially through the fan wheel; it passes first into a space between the fan wheel and the engine unit, where it is discharged radially.
Not only does the designer of such axial fans have to meet high requirements nowadays in respect of technical data such as generation of pressure of efficiency; but physiological aspects such as noise nuisance also have to be considered increasingly, thus making the requirements still more complex.
The noises from these fans consist mainly of the broad band or virtex noise and the particularly penetrating sound of the fan, the frequency of which corresponds to the product of the fan wheel speed and the number of fins. A reduction in the noise has been achieved by arranging the fins at unequal intervals on the hub of the fan wheel. Although this has diminished the unpleasant sound of the fan it has adversely affected flow conditions.